This invention relates to mechanism for preventing the build-up of gaseous combustion products in the crankcase system of an internal combustion engine, and the removal of such combustion products before they can contaminate the engine oil, by the application of a vacuum force on the crankcase system. The mechanism serves to replace the conventional positive crankcase ventilation (PCV) system now in general use.
Prior to my invention, others have developed various mechanisms and fluid systems for removing blowby vapors from crankcase areas of internal combustion engines. The term "blowby vapors" herein refers to vapors developed during the combustion process that escape from the combustion chamber across the piston rings, rather than through the exhaust passage.
Such blowby vapors are undesired in that they can build up to produce a pressurized condition in the crankcase, leading to possible leakage of lubricant across the main (crankshaft) seals and/or through the gasket joint between the cylinder block and oil pan.
Such blowby vapors are also undesirable in the crankcase because they can react with the hot oil to form oxides and varnishes; in some cases a sludge build-up occurs as a result of condensation of blowby water vapor into the crankcase oil, especially in cooler engine oil. This interferes with oil flow and/or adversely affects the lubricant action of oil being circulated through the engine. In some cases, the blowby vapors containing unburned fuel act as a dilutant for the oil, thereby adversely affecting the oil film thickness on bearing surfaces.
In a known positive crankcase ventilation (PCV) system, a throttled flow of blowby vapors is drawn from the engine valve (rocker arm) chamber through a small passage leading to a point in the air induction duct downstream from the throttle valve. Vacuum force in the induction duct draws blowby vapors from the rocker arm chamber into the duct for assimilation with the air-fuel mixture being fed to the combustion chamber.
The blowby vapor flow is throttled or controlled by a spring-biased PCV valve in the aforementioned passage. The valve is arranged for movement toward or away from a metering orifice formed in the PCV valve housing. The spring urge the valve element toward an open position (away from the metering orifice) in opposition to the action of the vacuum force. At low manifold vacuum, a relatively high flow rate is achieved; at high manifold vacuum, the valve element is drawn into the metering orifice to reduce the flow rate.
A problem with the described system is adequate control of the blowby vapor flow rate. If a weak spring is used, the valve element will close at medium manifold vacuum force, thereby preventing any flow under high vacuum force conditions. If a strong spring is used, the valve element may remain open under high manifold vacuum conditions, thereby producing excessively high flow rates, resulting in a lean fuel/air mixture.
The conventional system employs an air intake passage from the engine air cleaner to the rocker arm chamber. Under high vacuum conditions, air flows from the air cleaner through the air intake passage into the rocker arm chamber, thereby relieving the vacuum force; the added air flow undesirably reduces the blowby vapor flow rate and also contributes to excessively lean fuel/air mixtures. Under superatmospheric and/or low vacuum conditions, blowby vapors may flow in reverse direction from the rocker arm chamber through the air intake passage into the air cleaner.
In tests performed on a worn engine equipped with the described system, I found that the vacuum produced in the rocker arm chamber was relatively low, less than four-tenth inches of mercury. I believe this relatively low vacuum force to be insufficient for proper venting of the blowby vapors, especially under high load, or high acceleration conditions, or on older worn engines, all situations where substantial quantities of blowby vapors are generated at a high rate.
The principal object of my invention is to provide a crankcase venting mechanism wherein substantial vacuum forces are maintained, e.g., one to fifteen inches of mercury.
Another object of my invention is to provide a crankcase venting mechanism wherein the high vacuum force is maintained within safe limits, i.e., below some predetermined value suitable to engine design.
A further object is to provide a crankcase venting mechanism that has a partially sealed character, whereby there is no normally open passage for introducing atmospheric air pressure into the crankcase mechanism.
As a result of maintaining a controlled vacuum on the crankcase and oil system, two significant benefits are achieved:
1. all engine oil leaks within the crankcase, valve cover, and timing cover are abated, which includes bearing seals, gaskets, hose connections and diaphrams, and
2. the crankcase oil is maintained in a cleaner condition because (a) blowby vapors are kept in a vapor state under the reduced pressure and are less likely to condense into and contaminate the engine and crankcase oil, (b) under reduced pressure the hot oil is less likely to oxidize to form undesired products, and (c) under reduced pressure the total concentration (per unit volume) of blowby vapors is proportionally reduced and consequently is less likely to condense in the engine and crankcase oil.